1. Technical Field of the Invention
The present invention relates to devices and methods for restraining vehicles, and more particularly, to vehicle restraints for releasably securing vehicles to structures.
2. Description of the Related Art
Vehicle restraints are used to secure vehicles (e.g., trucks and/or trailers) to structures such as warehouses and loading docks. These devices secure vehicles to structures so that they cannot be moved except when these devices are intentionally released. One such device employs a hook to engage a portion of the vehicle. A motor drives the hook from a disengaged position to an engaged position to secure the vehicle to the structure. This engagement allows heavy equipment and personnel to enter and exit the vehicle without the vehicle separating from the loading dock.
Some vehicle restraints actuate the motor that moves the hook for a pre-determined period of time. The period of time, for example, may correspond to the amount of time it takes for the hook to reach its highest elevated position. Depending on the height of the engaging portion of a vehicle, the motor may attempt to drive the hook even after the hook is engaged. Vehicle restraints of this type may compensate for this condition by utilizing a slip clutch which permits the driveshaft of the motor to "free wheel" or continue to rotate even after the hook is engaged.
A known problem with this type of vehicle restraint is that varying loads, such as when heavy equipment is driven onto and off of a vehicle or when freight is loaded or unloaded from a vehicle, create excessive up-and-down motions or vibrations that can cause the clutch to slip and the hook to become disengaged. If left uncorrected, the vehicle could separate from the structure jeopardizing the safety of personnel and the condition of the equipment.
A known approach to overcome this problem monitors the engagement between the hook and the vehicle. When the hook becomes disengaged from the vehicle, the vehicle restraint may activate an alarm or automatically actuate the motor to drive the hook back to the engaged position. Unfortunately, should this condition occur regularly, the vehicle restraint motor and clutch may prematurely wear, and thus require frequent replacement or repair.